1. Field of the Invention
This invention relates to power supplies. More particularly, this invention relates to improved circuitry for use with chopper power supplies.
2. Description of the Prior Art
Chopper converter power supplies are useful for converting a D.C. input into a new D.C. voltage or an A.C. voltage of a desired frequency. This result is achieved by passing the input D.C. voltage through a series of switches thereby simulating an A.C. voltage which is impressed upon the primary of a transformer. The secondary output voltage is dependent of course upon the ratio of the number of the windings of the primary to the secondary, while the frequency of the output voltage is dependent upon the rate of switching of the input D.C. voltage. Where the chopper is driven by high frequency switching signals, an equivalent high output frequency can be achieved.
One of the primary difficulties encountered with chopper-type devices is the high fly-back voltage which appears at the inputs of the chopper circuit. More specifically, when an input to the chopper circuit makes a transition from the "on" state to the "off" state, the energy stored in the inductor feeding that input is released, resulting in an unacceptably high voltage at that input which could potentially damage the voltage chopper circuitry. One solution has been to place a series zener diode and resistor across the input choke to limit the amplitude of the fly-back voltage. While this may be effective at low chopper frequencies, the efficiency of the circuit with regard to power transmission drops as the frequency increases. Ideally, it would be desirable to capture the energy stored in the inductors and pass it through to the chopper circuit.